Evaporative Air Cooler: How It Works in a Room

An evaporative portable cooler pulls air across a water-wetted pad. Evaporation absorbs heat from the airflow, but the unit also adds moisture and needs ventilation to avoid recirculating increasingly humid air.

It generally needs ventilation so humid indoor air can escape. Australian Government guidance notes that portable evaporative coolers may lose effectiveness if they recirculate indoor air without airflow outside.

It is less effective when humidity is high because the air has less capacity to take up more water vapour. The Australian Government says evaporative cooling works well in low-humidity inland regions.

An evaporative cooler uses water evaporation, while an air conditioner transfers heat through a refrigeration cycle. Portable air conditioners also need an exhaust duct through an open window.